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Microwave ablation (MWA) plays a crucial role in non-surgical liver cancer treatment, but the existing efficacy evaluation tools lack the characteristics of being real-time, non-invasive, and efficient. As an emerging imaging technology, thermoacoustic imaging (TAI) has attracted extensive clinical attention for its excellent merits, which combine the advantages of high contrast in microwave imaging and high resolution in ultrasound imaging. Particularly, the application of a circular scanned single-channel data acquisition system maximizes the capture of thermoacoustic signals, thereby providing more comprehensive image information and rendering reconstructed images closer to reality. This study aimed to verify the feasibility of TAI in non-invasive evaluation of the efficacy of MWA on ex vivo porcine liver and in vivo rabbit liver. During the experiments, ultrasound is used to cross-verify the results of TAI to ensure the accuracy and reliability of the method. Additionally, by altering the thickness of porcine liver tissue to increase the distance (from 0 mm to 80 mm) between the horn antenna and the target (soy sauce tube), TAI is used to observe the change of the image signal-to-noise ratio to preliminarily explore the imaging depth of TAI. The results of ex and in vivo experiments can not only promote the clinical application of TAI, but also be expected to provide a more accurate and reliable efficacy assessment method for MWA in liver cancer treatment. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MTI) has the advantages of high resolution, high contrast, non-ionization, and non-invasive. Recently, MTI was used in the field of breast cancer screening. In this paper, based on the finite element method (FEM) and COMSOL Multiphysics software, a three-dimensional breast cancer model suitable for exploring the MTI process is proposed to investigate the influence of Young's modulus (YM) of breast cancer tissue on MTI. It is found that the process of electromagnetic heating and initial pressure generation of the entire breast tissue is earlier in time than the thermal expansion process. Besides, compared with normal breast tissue, tumor tissue has a greater temperature rise, displacement, and pressure rise. In particular, YM of the tumor is related to the speed of thermal expansion. In particular, the larger the YM of the tumor is, the higher the heating and contraction frequency is, and the greater the maximum pressure is. Different Young's moduli correspond to different thermoacoustic signal spectra. In MTI, this study can be used to judge different degrees of breast cancer based on elastic imaging. In addition, this study is helpful in exploring the possibility of microwave-induced thermoacoustic elastic imaging (MTAE). [ABSTRACT FROM AUTHOR]

Microwave ablation (MWA) plays a crucial role in non-surgical liver cancer treatment, but the existing efficacy evaluation tools lack the characteristics of being real-time, non-invasive, and efficient. As an emerging imaging technology, thermoacoustic imaging (TAI) has attracted extensive clinical attention for its excellent merits, which combine the advantages of high contrast in microwave imaging and high resolution in ultrasound imaging. Particularly, the application of a circular scanned single-channel data acquisition system maximizes the capture of thermoacoustic signals, thereby providing more comprehensive image information and rendering reconstructed images closer to reality. This study aimed to verify the feasibility of TAI in non-invasive evaluation of the efficacy of MWA on ex vivo porcine liver and in vivo rabbit liver. During the experiments, ultrasound is used to cross-verify the results of TAI to ensure the accuracy and reliability of the method. Additionally, by altering the thickness of porcine liver tissue to increase the distance (from 0 mm to 80 mm) between the horn antenna and the target (soy sauce tube), TAI is used to observe the change of the image signal-to-noise ratio to preliminarily explore the imaging depth of TAI. The results of ex and in vivo experiments can not only promote the clinical application of TAI, but also be expected to provide a more accurate and reliable efficacy assessment method for MWA in liver cancer treatment.

Microwave-induced thermoacoustic imaging (MTI) has the advantages of high resolution, high contrast, non-ionization, and non-invasive. Recently, MTI was used in the field of breast cancer screening. In this paper, based on the finite element method (FEM) and COMSOL Multiphysics software, a three-dimensional breast cancer model suitable for exploring the MTI process is proposed to investigate the influence of Young’s modulus (YM) of breast cancer tissue on MTI. It is found that the process of electromagnetic heating and initial pressure generation of the entire breast tissue is earlier in time than the thermal expansion process. Besides, compared with normal breast tissue, tumor tissue has a greater temperature rise, displacement, and pressure rise. In particular, YM of the tumor is related to the speed of thermal expansion. In particular, the larger the YM of the tumor is, the higher the heating and contraction frequency is, and the greater the maximum pressure is. Different Young’s moduli correspond to different thermoacoustic signal spectra. In MTI, this study can be used to judge different degrees of breast cancer based on elastic imaging. In addition, this study is helpful in exploring the possibility of microwave-induced thermoacoustic elastic imaging (MTAE).

Background: As an emerging hybrid imaging modality, microwave‐induced thermoacoustic imaging (MITAI) provides high contrast and deep tissue penetration, and has been extensively applied in cancer diagnosis, arthritis detection, and brain research. However, the previous studies had a limited spatial resolution of about 0.45–1.5 mm. Purpose: Here, we describe a microwave‐induced thermoacoustic microscopy (MITAM) system to help overcome the resolution limitation of current MITAI to image more subtle tissue features. On this basis, this paper applies MITAM to the thin skin and to demonstrate the potential of MITAM in detecting scleroderma. Methods: To achieve high resolution, short pulse width microwave (pulse width: 70 ns) and high‐frequency ultrasonic point‐focused transducer (center frequency: 25 MHz) were used to build the MITAM system. Two parallel copper wires with a diameter of 90 μm in the X/Y plane and Y/Z plane were imaged to estimate X/Y/Z resolution. Nine Balb/c mice were randomly divided into three groups and injected with different concentrations of bleomycin to induce scleroderma models. Their ex vivo skins were then imaged by our MITAM system. Visual observations were performed on the 3‐dimensional skins MITAM images. And the mean value, Standard deviation, quartile distance, and signal‐to‐noise ratio were calculated to verify the results of the qualitative observations. Hematoxylin‐Eosin (HE) and Masson staining were used to validate the findings of the MITAM. Results: The thickness of each imaged skin was measured to be about 450 μm. As an organ composed of multiple layers of tissues, the skin needs to be imaged at high resolution for the detection of related diseases. The results obtained showed that the improved resolution (68 μm in the Z‐axis and 135 μm in the X‐axis/Y‐axis) of MITAM over conventional MITAI allowed us to differentiate scleroderma skins from normal skins and to identify the severity of scleroderma skins, consistent with the pathological findings of these skins. Conclusions: The preliminary results obtained indicate that the MITAM can relieve the resolution limitation of traditional MITAI and has the potential to detection scleroderma. However, the transmission‐type MITAM mentioned in this paper is difficult to image in vivo due to the narrow area between the antenna and the transducer. In the future, a reflective scanning MITAM will be constructed to detect scleroderma in vivo. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MTAI) has emerged as a potential biomedical imaging modality with over 20-year growth. MTAI typically employs pulsed microwave as the pumping source, and detects the microwave-induced ultrasound wave via acoustic transducers. Therefore, it features high acoustic resolution, rich electromagnetic contrast, and large imaging depth. Benefiting from these unique advantages, MTAI has been extensively applied to various fields including pathology, biology, material and medicine. Till now, MTAI has been deployed for a wide range of biomedical applications, including cancer diagnosis, joint evaluation, brain investigation and endoscopy. This paper provides a comprehensive review on (1) essential physics (endogenous/exogenous contrast mechanisms, penetration depth and resolution), (2) hardware configurations and software implementations (excitation source, antenna, ultrasound detector and image recovery algorithm), (3) animal studies and clinical applications, and (4) future directions. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MTAI) is a promising alternative for breast tumor detection due to its deep imaging depth, high resolution, and minimal biological hazards. However, due to the bulky size and complicated system configuration of conventional benchtop MTAI, it is limited to imaging various anatomical sites and its application in different clinical scenarios. In this study, a handheld MTAI system equipped with a compact impedance matching microwave-sono and an ergonomically designed probe was presented and evaluated. The probe integrates a flexible coaxial cable for microwave delivery, a miniaturized microwave antenna, a linear transducer array, and wedge-shaped polystyrene blocks for efficient acoustic coupling, achieving microwave illumination and ultrasonic detection coaxially, and enabling high signal-to-noise ratio (SNR). Phantom experiments demonstrated that the maximum imaging depth is 5 cm (SNR = 8 dB), and the lateral and axial resolutions are 1.5 mm and 0.9 mm, respectively. Finally, three healthy female volunteers of different ages were subjected to breast thermoacoustic tomography and ultrasound imaging. The results showed that the h-MTAI data are correlated with the data of ultrasound imaging, indicating the safety and effectiveness of the system. Thus, the proposed h-MTAI system might contribute to breast tumor screening. [ABSTRACT FROM AUTHOR]

Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3 GHz, 3.0 GHz, and 5.3 GHz, and the lengths of copper wires are separately set to 11 cm, 5 cm, and 2.5 cm, the maximum SAR distribution and energy coupling efficiency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11 cm, 4.77 cm, and 2.7 cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MTAI) has emerged as a potential biomedical imaging modality with over 20-year growth. MTAI typically employs pulsed microwave as the pumping source, and detects the microwave-induced ultrasound wave via acoustic transducers. Therefore, it features high acoustic resolution, rich electromagnetic contrast, and large imaging depth. Benefiting from these unique advantages, MTAI has been extensively applied to various fields including pathology, biology, material and medicine. Till now, MTAI has been deployed for a wide range of biomedical applications, including cancer diagnosis, joint evaluation, brain investigation and endoscopy. This paper provides a comprehensive review on (1) essential physics (endogenous/exogenous contrast mechanisms, penetration depth and resolution), (2) hardware configurations and software implementations (excitation source, antenna, ultrasound detector and image recovery algorithm), (3) animal studies and clinical applications, and (4) future directions.

Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3[Formula: see text]GHz, 3.0[Formula: see text]GHz, and 5.3[Formula: see text]GHz, and the lengths of copper wires are separately set to 11[Formula: see text]cm, 5[Formula: see text]cm, and 2.5[Formula: see text]cm, the maximum SAR distribution and energy coupling efficiency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11[Formula: see text]cm, 4.77[Formula: see text]cm, and 2.7[Formula: see text]cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.

Microwave-induced thermoacoustic imaging (MTAI) has been widely used in biomedical science, and has the potential as an auxiliary measure for clinical diagnosis and treatment. Recently, there are increasing interests in using ultrashort microwave-pumped thermoacoustic imaging techniques to obtain high-efficiency, high-resolution images. However, the traditional imaging system can only provide uniform radiation in a relatively small area, which limits their large field of view in clinical applications (such as whole-breast imaging, brain imaging). To address this problem, we propose an ultrashort pulse microwave thermoacoustic imaging device with a large size aperture antenna. The system can provide a microwave radiation area of 40 cm × 27 cm and a uniform imaging view of 14 cm × 14 cm. With 7 cm imaging depth and a 290 μm resolution. The practical feasibility of the system for breast tumor screening is tested in phantoms with different shapes and in an ex vivo human breast tumor which is embedded in the excised breast of an ewe (π × 5 cm × 5 cm). The tumor can be identified with a contrast of about 1:2. The results demonstrate that the dedicated MTAI system with the uniform large field of view, high imaging resolution, and large imaging depth have the potential for clinical routine breast screening. [ABSTRACT FROM AUTHOR]

Thermoacoustic imaging is a crossbred approach taking advantages of electromagnetic and ultrasound disciplines, together. A significant number of current medical imaging strategies are based on reconstruction of source distribution from information collected by sensors over a surface covering the region to be imaged. Reconstruction in thermoacoustic imaging depends on the inverse solution of thermoacoustic wave equation. Homogeneous assumption of tissue to be imaged results in degradation of image quality. In our paper, inverse solution of the thermoacoustic wave equation using layered tissue model consisting of concentric annular layers on a cylindrical cross-section is investigated for cross-sectional thermoacustic imaging of breast and brain. By using Green’s functions and surface integral methods we derive an exact analytic inverse solution of thermoacoustic wave equation in frequency domain. Our inverse solution is an extension of conventional solution to layered cylindrical structures. By carrying out simulations, using numerical test phantoms consisting of thermoacoustic sources distributed in the layered model, our layered medium assumption solution was tested and benchmarked with conventional solutions based on homogeneous medium assumption in frequency domain. In thermoacoustic image reconstruction, where the medium is assumed as homogeneous medium, the solution of nonhomogeneous thermoacoustic wave equation results in geometrical distortions, artifacts and reduced image resolution due to inconvenient medium assumptions.

In situ image guidance is one of the key techniques for accurate diagnosis and treatment in clinical medicine. Conventional imaging techniques such as CT, MRI provide critical information for diagnosis and treatment planning, but are less practical due to either technical complexity or ionizing radiation-related safety. Microwave-pumped thermoacoustic imaging (MTAI) is a promising alternative to real-time bioimaging due to its deep imaging depth, high resolution and minimal biological hazards. More importantly, by mapping the distribution of microwave absorbers, this method can also provide a new perspective for noninvasively observing the anatomy and functional structure of the target. In this work, we introduce a concept of in situ MTAI guidance by combining MTAI and an accurate spatial definition of invasive apparatus used in potential procedures. By mounting tiny MTAI beacons on the apparatus, it is possible to accurately reconstruct the relative position of the device to the target tissue for either real time visual guidance or as the foundation for potential automated procedures. The image quality including its applicable depth and resolution, the accuracy of the device localization is analyzed and tested with simulated breast tumor to demonstrate the capacity of the proposed technique. With refined adaptation for potential applications, this technique may provide a novel approach for a broad range of medical and biological applications.

Microwave-induced thermoacoustic imaging (MI-TAI) remains one of the focus of attention among biomedical imaging modalities over the last decade. However, the transmission and distribution of microwave inside bio-tissues are complicated, thus result in severe artifacts. In this study, to reveal the underlying mechanisms of artifacts, we deeply investigate the distribution of specific absorption rate (SAR) inside tissue-mimicking phantoms with varied morphological features using both mathematical simulations and corresponding experiments. Our simulated results, which are confirmed by the associated experimental results, show that the SAR distribution highly depends on the geometries of the imaging targets and the polarizing features of the microwave. In addition, we propose the potential mechanisms including Mie-scattering, Fabry-Perot-feature, small curvature effect to interpret the diffraction effect in different scenarios, which may provide basic guidance to predict and distinguish the artifacts for TAI in both fundamental and clinical studies. [ABSTRACT FROM AUTHOR]

Purpose: Most of existing thermoacoustic imaging (TAI) studies generally utilized a linear modulator‐based high peak power magnetron generator (MG) for efficient TA signal excitation. However, a linear modulator‐based MG is bulky and expensive. Here we present a low‐cost and compact thermoacoustic imaging (TAI) system based on a miniaturized MG. Methods: The MG is based on solid‐state modulator and operates at 3.05 ± 0.025 GHz, with a peak power of up to 60 kW and adjustable pulse duration from 70 to 600 ns. The dimensions and weight of this MG are 350 × 210 × 70 mm3 (Width × Length × Height) and 7.5 kg, respectively. Results: The spatial resolution of the miniaturized MG‐based TAI system is determined to be from 0.3 to 1.4 mm using controlled phantom experiments. The system is further evaluated using in vivo experiments where the finger joints and vasculature in the forearm and opisthenar of human participants are successfully imaged. Conclusions: This study suggests that the miniaturized MG based TAI systems can be used for in vivo joint and vascular imaging with multiscale resolutions (0.3–1.4 mm). [ABSTRACT FROM AUTHOR]

Pulse microwave excite thermoacoustic (TA) Shockwave to destroy tumor cells in situ. This has promising applications for precise tumor therapy in deep tissue. Nanoparticle (NP) with high microwave-acoustic conversion is the key to enhance the efficiency of therapy. In this study, we firstly developed defect-rich titanium nitride nanoparticles (TiN NPs) for pulse microwave excited thermoacoustic (MTA) therapy. Due to a large number of local structural defects and charge carriers, TiN NPs exhibit excellent electromagnetic absorption through the dual mechanisms of dielectric loss and resistive loss. With pulsed microwave irradiation, it efficiently converts the microwave energy into shockwave via thermocavitation effect, achieving localized mechanical damage of mitochondria in the tumor cell and yielding a precise antitumor effect. In addition to the therapeutic function, the NP-mediated TA process also generates images that provide valuable information, including tumor size, shape, and location for treatment planning and monitoring. The experimental results showed that the TiN NPs could be efficiently accumulated in the tumor via intravenous infusion. With the deep tissue penetration characteristics of microwave, the proposed TiN-mediated MTA therapy effectively and precisely cures tumors in deep tissue without any detectable side effects. The results indicated that defect-rich TiN NPs are promising candidates for tumor therapy. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (MI-TAI) remains one of the focus of attention among biomedical imaging modalities over the last decade. However, the transmission and distribution of microwave inside bio-tissues are complicated, thus result in severe artifacts. In this study, to reveal the underlying mechanisms of artifacts, we deeply investigate the distribution of specific absorption rate (SAR) inside tissue-mimicking phantoms with varied morphological features using both mathematical simulations and corresponding experiments. Our simulated results, which are confirmed by the associated experimental results, show that the SAR distribution highly depends on the geometries of the imaging targets and the polarizing features of the microwave. In addition, we propose the potential mechanisms including Mie-scattering, Fabry-Perot-feature, small curvature effect to interpret the diffraction effect in different scenarios, which may provide basic guidance to predict and distinguish the artifacts for TAI in both fundamental and clinical studies.

Imaging technology plays an important role in the diagnosis, treatment and monitoring of diseases. As a new non-ionizing and non-invasive biomedical imaging technology, thermoacoustic imaging combines the advantages of microwave imaging high contrast and ultrasound imaging high resolution. Because of its ability to use endogenous contrast agents (such as water and ions) or multiple exogenous contrast agents (or both) to provide structure, function, and molecular information, it has been shown in pre-clinical and clinical applications. huge potential. In recent decades, due to the continuous development of microwave radiation sources and ultrasound hardware, thermoacoustic imaging technology has been widely used in the field of biomedical imaging. This article explains the basic principles and imaging characteristics of thermoacoustic imaging, introduces the application of thermoacoustic imaging technology in biomedicine in recent years, the current advantages and research status in solving corresponding clinical problems, and finally focuses on the current status of thermoacoustic imaging technology. There are challenges faced in biomedicine, and the technology is prospected. [ABSTRACT FROM AUTHOR]

The large differences of electrical characteristics can be used to reflect the physiological and pathological changes about biological tissues, and it can provide evidence for the early diagnosis and treatment of cancer in potential applications. This paper describes a method called Applied Current Thermoacoustic Imaging (ACTAI) and explores the theory and demonstrates a low conductivity numerical simulation and fresh pork experimental studies. In this paper, firstly, the principle of ACTAI is studied. In ACTAI, a target is applied with a microsecond width Gaussian pulse current. Then the target absorbs Joule heat and expands instantaneously, sending out thermoacoustic waves. The waves contain the conductivity information of the target. The waves received by sound transducers are processed by the time inversion method to reconstruct the sound source distribution of the target to illustrate the conductivity information of the target. Secondly, a square model with low conductivity was used as a target to conduct numerical simulation of ACTAI. Lastly, a fresh pork experiment study was conducted. The presented experimental results suggest that ACTAI can identify the conductivity changes information of the target with perfect imagery contrast and deep penetration. The ACTAI modality would benefit from the noncontact measurement and can be convenient for clinical application. [ABSTRACT FROM AUTHOR]

In situ image guidance is one of the key techniques for accurate diagnosis and treatment in clinical medicine. Conventional imaging techniques such as CT, MRI provide critical information for diagnosis and treatment planning, but are less practical due to either technical complexity or ionizing radiation-related safety. Microwave-pumped thermoacoustic imaging (MTAI) is a promising alternative to real-time bioimaging due to its deep imaging depth, high resolution and minimal biological hazards. More importantly, by mapping the distribution of microwave absorbers, this method can also provide a new perspective for noninvasively observing the anatomy and functional structure of the target. In this work, we introduce a concept of in situ MTAI guidance by combining MTAI and an accurate spatial definition of invasive apparatus used in potential procedures. By mounting tiny MTAI beacons on the apparatus, it is possible to accurately reconstruct the relative position of the device to the target tissue for either real time visual guidance or as the foundation for potential automated procedures. The image quality including its applicable depth and resolution, the accuracy of the device localization is analyzed and tested with simulated breast tumor to demonstrate the capacity of the proposed technique. With refined adaptation for potential applications, this technique may provide a novel approach for a broad range of medical and biological applications. [ABSTRACT FROM AUTHOR]

Noninvasive extraction of tissue conductivity distribution is important in brain imaging and cancer detection. Here we present an improved method that can accurately image tissue conductivity using tomographically measured microwave-induced thermoacoustic data. Our reconstruction algorithm is first tested using simulations, and then validated using tissue phantom experiments where saline-containing tubes are used as target(s) with various target sizes, positions and conductivities. The average error of reconstruction for the simulations is reduced from 4.87% to 1.38% compared with the previous algorithm. The experimental results obtained suggest that accurate quantitative thermoacoustic imaging would provide a potential tool for precision medicine. [ABSTRACT FROM AUTHOR]

We derived analytical forward and inverse solution of thermoacoustic wave equation for nonhomogeneous medium. We modelled the nonhomogeneous medium as a multi-layer planar medium and defined initial conditions, continuity conditions on the layer boundaries and radiation conditions at infinity assuming the source distribution existing in all layers. These solutions of thermoacoustic wave equation are based on the method of Green's functions for layered planar media. For qualitative testing and comparison of the point-spread functions associated with the homogeneous and layered solutions, we performed numerical simulations. Our simulation results showed that the conventional inverse solution based on homogeneous medium assumption, as expected, produced incorrect locations of point sources, whereas our inverse solution involving the multi-layer planar medium produced point sources at the correct source locations. Also, we examined whether the performance of our layered inverse solution is sensitive to medium parameters used as priority information in the measured data. Our inverse solutions based on multi-layer planar media are applicable for cross-sectional two-dimensional imaging of abdominal structure and the organs such as breast and skin. [ABSTRACT FROM AUTHOR]

Purpose: Conventional antenna used in thermoacoustic imaging (TAI) is often bulky, making it difficult to translate TAI from the bench to the clinic. In this paper, we proposed a handheld dipole antenna which will be a good candidate for the construction of a compact TAI system. Methods: Here, we propose a TAI system based on a handheld dipole antenna with an aperture of 6 cm and a weight of 230 g. Compensation of the electric field attenuation for such a system was also investigated. Results: Compared to the conventional open‐ended waveguide and pyramidal horn antenna used in TAI, our results reveal that the electric field attenuation induced distortion is effectively reduced by using the attenuation factor 1/r2 for compensation and that the handheld dipole antenna provides the highest efficiency of microwave delivery. Conclusions: This study suggests that the handheld dipole antenna has the potential to be utilized for the construction of a compact TAI system, making TAI more suitable for preclinical and clinical applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel nonlinear thermoacoustic imaging (NTAI) system is developed based on the temperature-dependent thermoelastic response under microwave irradiation. Specifically, we consider the high-pulse repetition frequency (HPRF) microwave regime, where the tissue temperature increases after microwave irradiation. In this circumstance, the temperature-dependent thermodynamic parameters of the tissue change; thus, the influence of absorbed microwave energy on the thermoacoustic (TA) amplitude is reflected in the change of thermodynamic parameters. Hence, this temperature dependence yields a nonlinear relationship between the TA amplitude and the absorbed microwave energy in the HPRF regime. In this paper, we obtain the nonlinear coefficient as a new parameter to distinguish biological tissues by performing differential measurements in the NTAI system. We further experimentally extract the nonlinear coefficient in phantom and ex vivo mouse, revealing the feasibility of applications in biological tissues identification with high contrast. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging (PAI) and thermoacoustic imaging (TAI) are two emerging biomedical imaging techniques that both utilize ultrasonic signals as an information carrier. Unique advantages of PAI and TAI are their abilities to provide high resolution functional information such as hemoglobin and blood oxygenation and tissue dielectric properties relevant to physiology and pathology. These two methods, however, may have a limited detection depth and lack of endogenous contrast. An exogenous contrast agent is often needed to effectively resolve these problems. Such agents are able to greatly enhance the imaging contrast and potentially break through the imaging depth limit. Furthermore, a receptor-targeted contrast agent could trace the molecular and cellular biological processes in tissues. Thus, photoacoustic and thermoacoustic molecular imaging can be outstanding tools for early diagnosis, precise lesion localization, and molecular typing of various diseases. The agents also could be used for therapy in conjugation with drugs or in photothermal therapy, where it functions as an enhancer for the integration of diagnosis and therapy. In this article, we present a detailed review about various exogenous contrast agents for photoacoustic and thermoacoustic molecular imaging. In addition, challenges and future directions of photoacoustic and thermoacoustic molecular imaging in the field of translational medicine are also discussed.

Intraoperative imaging (IOI) is performed to guide delineation and localization of regions of surgical interest. While oncological surgical planning predominantly utilizes x-ray computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US), intraoperative guidance mainly remains on surgeon interpretation and pathology for confirmation. Over the past decades however, intraoperative guidance has evolved significantly with the emergence of several novel imaging technologies, including fluorescence-, Raman, photoacoustic-, and radio-guided approaches. These modalities have demonstrated the potential to further optimize precision in surgical resection and improve clinical outcomes for patients. Not only can these technologies enhance our understanding of the disease, they can also yield large imaging datasets intraoperatively that can be analyzed by deep learning approaches for more rapid and accurate pathological diagnosis. Unfortunately, many of these novel technologies are still under preclinical or early clinical evaluation. Organizations like the Intra-Operative Imaging Study Group of the European Society for Molecular Imaging (ESMI) support interdisciplinary interactions with the aim to improve technical capabilities in the field, an approach that can succeed only if scientists, engineers, and physicians work closely together with industry and regulatory bodies to resolve roadblocks to clinical translation. In this review, we provide an overview of a variety of novel IOI technologies, discuss their challenges, and present future perspectives on the enormous potential of IOI for oncological surgical navigation. [ABSTRACT FROM AUTHOR]

This review describes emerging techniques within the last 5 years that employ ultrasound for detecting and staging malignancy, tracking metastasis, and guiding treatment. Ultrasound elastography quantifies soft tissue elastic properties that change as a tumor grows and proliferates. Hybrid imaging modalities that combine ultrasound with light or microwave energy provide novel contrast for mapping blood oxygen saturation, transport of particles through lymphatic vessels and nodes, and real-time feedback for guiding needle biopsies. Combining these methods with smart nanoparticles and contrast agents further promotes new paradigms for cancer imaging and therapy. [ABSTRACT FROM AUTHOR]

Patients who have implanted medical devices with long conductive leads are often restricted from receiving MRI scans due to the danger of RF-induced heating near the lead tips. Phantom studies have shown that this heating varies significantly on a case-by-case basis, indicating that many patients with implanted devices can receive clinically useful MRI scans without harm. However, the difficulty of predicting RF-induced lead tip heating prior to scanning prevents numerous implant recipients from being scanned. Here, we demonstrate that thermo-acoustic ultrasound (TAUS) has the potential to be utilized for a pre-scan procedure assessing the risk of RF-induced lead tip heating in MRI. A system was developed to detect TAUS signals by four different TAUS acquisition methods. We then integrated this system with an MRI scanner and detected a peak in RF power absorption near the tip of a model lead when transmitting from the scanner’s body coil. We also developed and experimentally validated simulations to characterize the thermo-acoustic signal generated near lead tips. These results indicate that TAUS is a promising method for assessing RF implant safety, and with further development, a TAUS pre-scan could allow many more patients to have access to MRI scans of significant clinical value. [ABSTRACT FROM PUBLISHER]

Microwave-induced thermoacoustic imaging (TAI) is a noninvasive modality based on the differences in microwave absorption of various biological tissues. TAI has been extensively researched in recent years, and several studies have revealed that TAI possesses advantages such as high resolution, high contrast, high imaging depth and fast imaging speed. In this paper, we reviewed the development of the TAI technique, its excitation source, data acquisition system and biomedical applications. It is believed that TAI has great potential applications in biomedical research and clinical study.

We present for the first time in vivo imaging of rat brain using microwave-induced thermoacoustic tomography (TAT). The in vivo imaging of rat brain was realized through an unconventional delivery of microwave energy from the front of rat brain (while the transducer was scanned along coronal plane of the animal brain), which maximized the microwave penetration into the brain. In addition, we found that the imaging contrast was highly dependent on the direction of the electric field polarization (EFP) and that more tissue structures/compositions could be revealed when both X- and Y-EFPs were used for TAT. The in vivo TAT images of rat brain obtained were compared with the 3.0 T MRI images and histological photographs, and numerous important brain anatomical structures were identified. An example of our TAT approach for imaging a foreign object embedded in a rat brain was also demonstrated. This study suggests that TAT has a great potential to be used in neuroscience studies and in noninvasive imaging of brain disorders.

We present for the first time in vivo imaging of rat brain using microwave-induced thermoacoustic tomography (TAT). The in vivo imaging of rat brain was realized through an unconventional delivery of microwave energy from the front of rat brain (while the transducer was scanned along coronal plane of the animal brain), which maximized the microwave penetration into the brain. In addition, we found that the imaging contrast was highly dependent on the direction of the electric field polarization (EFP) and that more tissue structures/compositions could be revealed when both - and -EFPs were used for TAT. The in vivo TAT images of rat brain obtained were compared with the 3.0 T MRI images and histological photographs, and numerous important brain anatomical structures were identified. An example of our TAT approach for imaging a foreign object embedded in a rat brain was also demonstrated. This study suggests that TAT has a great potential to be used in neuroscience studies and in noninvasive imaging of brain disorders. [ABSTRACT FROM AUTHOR]

Microwave-induced thermoacoustic imaging (TAI) is a noninvasive modality based on the differences in microwave absorption of various biological tissues. TAI has been extensively researched in recent years, and several studies have revealed that TAI possesses advantages such as high resolution, high contrast, high imaging depth and fast imaging speed. In this paper, we reviewed the development of the TAI technique, its excitation source, data acquisition system and biomedical applications. It is believed that TAI has great potential applications in biomedical research and clinical study. [ABSTRACT FROM AUTHOR]

Purpose To study the possibility of thermoacoustic imaging ( TAI) toward hemorrhagic stroke detection. Methods A single-transducer circular-scanning TAI system was used for data collection. An agar powder-based, tissue-mimicking phantom enclosed by a human skull was applied to simulate the brain for thermoacoustic imaging of hemorrhagic stroke. Results Several phantom experiments mimicking hemorrhagic stroke detection were conducted, and the results showed that 'hemorrhagic' targets as small as 0.9 mm in diameter could be detected. Conclusions This study suggests that TAI has the potential to be used for noninvasive hemorrhagic stroke detection and identification of hemorrhagic from ischemic stroke. [ABSTRACT FROM AUTHOR]

Purpose: Knee joint is one of the largest and most complex joints of the body. Knee joint diseases are common, and current clinical imaging technologies such as x-ray computed tomography, magnetic resonance imaging, and ultrasound imaging have limitations in the diagnosis of knee joint diseases. Emerging imaging technologies such as diffuse optical tomography and photoacoustic imaging (PAI) have been applied to the detection of osteoarthritis (OA). However, they are limited to small joints such as the finger and difficult to be used for large joints such as the knee. Thermoacoustic imaging (TAI), also an emerging modality, provides high contrast and deep tissue penetration. Here, the authors apply TAI to the knee joint and demonstrate the potential of TAI for imaging large joints. Methods: Adult New Zealand male rabbits (average weight = 2 kg) were chosen for this study. In a TAI experiment, a rabbit was placed in a holder to keep in a genuflex position after being injected with pentobarbital through its ear margin intravenous (30 mg/kg). The holder and the rabbit were then positioned under the horn antenna of the TAI system for signal acquisition and image reconstruction. After the experiment, the imaged knee joint was dissected and photographed. Identical procedures were performed for several rabbits (n = 4). Finally, detailed comparative analyses between TAI images and anatomical pictures of the knee joint were conducted. Results: There were high similarities between the reconstructed TAI images and anatomical pictures of the knee joint, in terms of the shape and size of various knee joint tissues. TAI could clearly image ligament, fat pad, and other joint tissues. The differences in appearance of TAI images due to motion effect of the knee joint were also discussed. Conclusions: TAI could reveal details of rabbit knee joint in high resolution. As the recovered TAI images represent the dielectric property distributions of joint tissues, TAI may offer a new tool for noninvasive detection of joint diseases such as OA. [ABSTRACT FROM AUTHOR]

Imaging-guided percutaneous microwave thermotherapy has been regarded as an important alternative nonsurgical therapeutic strategy for hepatocellular carcinoma (HCC) that provides excellent local tumor control and favorable survival benefit. However, providing a high-resolution, real-time, and noninvasive imaging technique for intraoperative guidance and controlling postoperative residual tumor recurrence are urgent needs for the clinical setting. In this study, a cisplatin (CDDP)-loaded nanocapsule (NPs@CDDP) with microwave responsive property was prepared to simultaneously serve as a contrast agent of emerging thermoacoustic imaging and a sensitizing agent of microwave thermo-chemotherapy. Accompanying the enzymolysis in the tumor microenvironment, the NPs@CDDP responsively release l-arginine (l-Arg) and CDDP. l-Arg with excellent microwave-absorbing property allowed it to serve as a thermoacoustic imaging contrast agent for accurately delineating the tumor and remarkably increasing tumor temperature under ultralow power microwave irradiation. Apart from the chemotherapeutic effect, CDDP elevated the intracellular H 2 O 2 level through cascade reactions and further accelerated the continuous transformation of l-Arg to nitric oxide (NO), which endowed the NPs@CDDP with NO-generation capability. Notably, the high concentration of intracellular NO was proved to aggravate lipid peroxidation and greatly improved the efficacy of microwave thermo-chemotherapy. Thereby, NPs@CDDP was expected to serve as a theranostic agent integrating the functions of tumor microenvironment-responsive drug delivery system, contrast agent of thermoacoustic imaging, thermal sensitizing agent, and NO nanogenerator, which was promising to provide a potential imaging-guided therapeutic strategy for HCC.

We report the design of a real-time thermoacoustic (TA) scanner dedicated to imaging deep breast tumors and investigate its imaging performance. The TA imaging system is composed of an ultrashort microwave pulse generator and a ring transducer array with 384 elements. By vertically scanning the transducer array that encircles the breast phantom, we achieve real-time, 3D thermoacoustic imaging (TAI) with an imaging speed of 16.7 frames per second. The stability of the microwave energy and its distribution in the cling-skin acoustic coupling cup are measured. The results indicate that there is a nearly uniform electromagnetic field in each XY-imaging plane. Three plastic tubes filled with salt water are imaged dynamically to evaluate the real-time performance of our system, followed by 3D imaging of an excised breast tumor embedded in a breast phantom. Finally, to demonstrate the potential for clinical applications, the excised breast of a ewe embedded with an ex vivo human breast tumor is imaged clearly with a contrast of about 1:2.8. The high imaging speed, large field of view, and 3D imaging performance of our dedicated TAI system provide the potential for clinical routine breast screening. [ABSTRACT FROM PUBLISHER]